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[16:00:18]

JAKE TAPPER, CNN ANCHOR: If Donald Trump wins tomorrow, will anything be able to stop him on his way to the nomination?

THE LEAD starts right now.

A full-on demolition derby. With one day until the South Carolina Republican primary, as all the candidates trade paint with Trump, is there any way Trump could blow a tire and not send the GOP into full- on panic mode?

On the other side, voters in Nevada poised to make this the wildest race in history for the Democrats too, as the Clinton machine tries to slow the Bern.

Plus, dozens dead as U.S. warplanes target ISIS 1,000 miles away from the Middle East in Libya, was another terrorist attack on the way?

Hello, everyone. I'm Jake Tapper. Welcome to THE LEAD.

In our politics lead, the question for our viewers, and among them, members of the Republican establishment, is Donald Trump about to become unstoppable in his quest for the nomination with this expected win in South Carolina?

The Republican front-runner answering supporters' questions at an event in Pawleys Island, South Carolina, this past hour. At a lunchtime event earlier, he served up a heaping helping of attacks on Ted Cruz, painting Senator Cruz as a puppet for special interests.

Trump is making three stops across the Palmetto State today. And, as you can see, he's not the only Republican with a packed schedule there.

CNN's Sunlen Serfaty is in Charleston, South Carolina.

Sunlen, last night, BuzzFeed published evidence that Donald Trump voiced support for the war in Iraq back in 2002 despite his current and many claims that he was an early opponent of the war. This is a major argument Trump makes about how sound his judgment is.

I haven't heard any of his Republican opponents raise this on the trail today. Am I wrong?

SUNLEN SERFATY, CNN NATIONAL CORRESPONDENT: No, that's absolutely right, Jake. None of his rivals have brought this up at all today on the campaign trail yet. This is a claim that Donald Trump himself repeats so often standing in front of voters saying that he was opposed early on to the invasion and to the Iraq War.

So, tonight, he is certainly struggling to explain this just one day before voters head to the polls.

(BEGIN VIDEOTAPE)

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: Here in South Carolina, these next 21 hours are going to decide a great deal.

SERFATY: The urgent pitches.

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: I'm different, because I have a chance to win New York. I have -- can you imagine? If you win New York, New York is...

SERFATY: In the final sprint in South Carolina.

TRUMP: You talk about people that lies, this Ted Cruz, this is the biggest liar I have ever seen.

SERFATY: Donald Trump now trying to de-escalate his feud with the pope.

TRUMP: They had him convinced that illegal immigration is like a wonderful thing.

SERFATY: Putting blame on the media instead.

TRUMP: I don't like fighting with the pope. I don't think it's a fight. I think he said something much softer than was originally reported by the media.

SERFATY: The Vatican today clarifying that the pope's comment was not a -- quote -- "personal attack" or an indication in how to vote, but Trump also on the defense struggling to explain his past stance on the Iraq War, BuzzFeed obtaining these comments Trump made to Howard Stern in 2002 supporting the invasion for Iraq.

HOWARD STERN, RADIO TALK SHOW HOST: Are you for invading Iraq?

TRUMP: Yes, I guess so. You know, I wish it was -- I wish the first time it was done correctly.

SERFATY: That much different than what Trump regularly tells voters on the campaign trail, that he opposed the invasion from the start.

TRUMP: I'm the one from 2002, 2003 said you shouldn't be doing it.

SERFATY: At the CNN town hall, Trump tried to explain.

ANDERSON COOPER, CNN ANCHOR: Do you remember saying that?

TRUMP: No. But, I mean, I could -- I could have said that. Nobody asked me. I wasn't a politician. It was probably the first time anybody asked me that question.

SERFATY: And today trying to clean it up.

TRUMP: I was with Howard Stern before the war, before, like many months before. And the first guy to ever ask me about Iraq was Howard Stern. And I said, no, I don't know, I guess so.

Then I started looking at it. Before the war started, I was against that war. I was against that war.

SERFATY: Meanwhile, the most intense South Carolina showdown is the fierce battle between Rubio and Cruz, each fighting to leave South Carolina with the upper hand as the alternative to Trump.

CRUZ: We have been through a wild, woolly election season.

SERFATY: Jeb Bush under pressure to finish strong here, campaigning with his mom.

BARBARA BUSH, FORMER FIRST LADY: Jeb has been a great son, great father, great husband.

SERFATY: And laying into nearly all of his rivals.

JEB BUSH (R), PRESIDENTIAL CANDIDATE: Donald Trump has never shown any interest in anybody else other than himself. And the two candidates that are gifted speakers, Marco Rubio and Ted Cruz, have shown nothing in their past that would suggest they could make a tough decision.

(END VIDEOTAPE)

SERFATY: And, today, Jeb Bush and his campaign are facing question after question. If you do not do well here, what is the path forward?

[16:05:00]

Bush for his part says he's only focused on today and tomorrow, but, certainly, Jake, he has a lot of pressure riding here in South Carolina.

TAPPER: All right, Sunlen Serfaty, thank you so much.

A historical first took place this week and it shows just how wild this presidential race has become that few people seem to even notice it. Within the space of just a few hours, two American presidents went after the Republican front-runner, Donald Trump. The first was the current president, Barack Obama, who assailed Mr. Trump directly.

(BEGIN VIDEO CLIP)

BARACK OBAMA, PRESIDENT OF THE UNITED STATES: I continue to believe Mr. Trump will not be president. And the reason is because I have a lot of faith in the American people. And I think they recognize that being president is a serious job. It's not hosting a talk show or a reality show. It's not promotion. It's not marketing.

(END VIDEO CLIP)

TAPPER: The second was Mr. Obama's predecessor, George W. Bush, campaigning for his brother, Jeb.

(BEGIN VIDEO CLIP)

GEORGE W. BUSH, FORMER PRESIDENT OF THE UNITED STATES: Strength is not empty rhetoric, it is not bluster, it is not theatrics. Real strength, strength of purpose, comes from integrity and character. And, in my experience, the strongest person usually isn't the loudest one in the room.

(CHEERING AND APPLAUSE)

TAPPER: And then, just for good measure, none other than Pope Francis weighed in on Mr. Trump, suggesting that Trump because he wants to build a wall at the U.S.-Mexican border is not Christian.

We don't even notice these things anymore, but it has never happened in American history before, at least as far as we could find, that in one week two presidents from different parties and a pope all criticized a presidential candidate.

Phil, we have all speculated that something Donald Trump said would ultimately ruin his chances, and now you have opposition from Barack Obama, George W. Bush, Pope Francis. If he wins tomorrow, is Mr. Trump unstoppable in his quest for the nomination?

PHIL MUSSER, FORMER ADVISER TO ROMNEY CAMPAIGN: No, he's not unstoppable at that point in time because there's a long, long, long way to go.

The nature of the process is such the delegates are going to be divided and really until March 1 or March 15, even more specifically, you can't make that. But, look, a good head of steam in South Carolina, a big win in Nevada caucus, which is a composition of a caucus that looks very different than the Iowa caucuses, it would be -- it would certainly be a healthy wind at his back.

But, look, this thing has got a lot of turns. Donald Trump took on Apple this afternoon. We will see how that one goes. So it's been a pretty amazing week in politics.

TAPPER: Right.

Before we get to Apple, S.E., I want to talk to you about this -- Donald Trump is out there on the stump talking about how he was an early opponent of the war in Iraq. Plenty of us when interviewing him say -- have said -- and I have said it at least twice -- we can't find any evidence that you opposed the war in 2003, 2004, sure, but not 2003. He kind of just ignores it.

Now BuzzFeed found evidence that he supported the war in 2002. Why aren't any of his opponents talking about this?

S.E. CUPP, CNN POLITICAL COMMENTATOR: Well, to you and I, this sounds like a smoking gun, but you and, I don't think, particularly understand the Trump phenomenon the way some other people seem to.

This does nothing to hurt him. And I think finally the other candidates seem to realize this isn't useful on the campaign trail to say Donald Trump kind of fibbed when he suggested he was the first to come out. I mean, this just doesn't do anything to deflate Trump's support.

So I think at this point, we're all so used to the flip-flops and the -- you know, the sort of half truths and outright lies that we don't even bother kind of making them a big deal anymore.

MUSSER: Yes. It's the issue that one of the concerns in the party if you look forward to the general is that there's just a treasure trove of opposition research on Donald Trump.

To be clear, I don't have a dog in this fight, but...

TAPPER: You want to win.

MUSSER: But we want Republicans to win.

And so one of the fears I have been hearing more and more and more is we really just scratched the tip of the iceberg relative to these kinds of things coming out. And so to the degree that they matter, they traditionally have mattered a lot, Mitt Romney and the 47 percent four years ago, but to S.E.'s point, we're just in completely uncharted waters with this political figure.

CUPP: And to your point, which is excellent, excellent research and a reminder of what an amazing week this has been, when President Obama, George W. Bush and the pope are attacking Donald Trump, all good for Donald Trump, every single one of those people.

TAPPER: Yes. It only helps.

(CROSSTALK)

TAPPER: I want to talk about the Apple thing.

A court order told Apple to build a back door to its software so that the FBI could get access to the San Bernardino terrorist's iPhone. This is something that Donald Trump said today that I think will actually be popular. Take a listen.

(BEGIN VIDEO CLIP) TRUMP: First of all, Apple ought to give the security for that phone, OK? What I think you ought to do is boycott Apple until such time as they give that security number.

(END VIDEO CLIP)

TAPPER: Now, I don't know if his boycott, his call for a boycott will work, but that is an easily understandable argument for a crowd during an election.

[16:10:08]

MUSSER: It is, but it's a little bit of a dangerous one too. OK?

Look, as a political consultant, I probably wouldn't advise my client to take on an iconic American brand when you have to remember we started this race with a candidate who represented probably 20 percent of the Republican Party with a libertarian kind of lane, right?

And that seems to have seized up as foreign affairs have pushed it down. But there are a lot of younger Republicans that really care about privacy, that care about this issue that could be really turned off by that message. Look no further than Nevada, the next stop down the line.

And I think you would find more of those types of people as you go closer to the coasts. So how it will play in the long term, I don't know. Fighting with Apple, I don't know.

TAPPER: Yes.

CUPP: I mean, it's a good guttural response.

TAPPER: Yes, national security, I want to be safe.

CUPP: Sure. But it really ignores the conversation that conservatives have been having for years about privacy, the NSA, Edward Snowden, all of these issues that I'm not sure Donald Trump was paying attention to, that I think remind some voters at least that this is not a cause for a black-and-white guttural response.

There's nuance here. It's complicated. You open this one Apple iPhone, you can open all iPhones.

TAPPER: Right, because you have build operating software to do it.

CUPP: Right.

(CROSSTALK)

MUSSER: When it becomes about you, the person, the individual, it's a very different prism than being about kind of a law and order national security question.

CUPP: But that also is a national security issue. It is both personal and national. So, again, I think Trump gets the easy win with the sort of knockout

black and white here's my response, but the nuanced answer is more appropriate. And that's what you're hearing from some of the other candidates.

TAPPER: Quickly, if you can, does Jeb Bush have to finish top three to continue credibly his campaign, do you think?

MUSSER: No, he needs to finish top four to finish -- I think move forward credibly. A fifth-place finish would be a disaster for Jeb Bush. He can finish fourth and move forward because he still has resources and he has resources backing him up on the outside.

The real thing that I think people are looking for is the margin and he has to be right there between third and fourth.

CUPP: He's got tons of money and infrastructure. I actually think he can go as long as he wants to go and just be the last establishment man standing and then really put up a fight against Cruz or Trump.

More on our politics lead now. Hillary Clinton telling Nevadans that unlike a certain somebody, she's not out there just promising voters free stuff. Instead, she says she wants to get things done -- as she tries to fend off a Bernie Sanders' victory tomorrow in the Nevada caucuses.

Bernie Sanders, meanwhile, accusing Clinton of cozying up to President Obama just to get African-American support.

Brianna, the polls have it very tight out there. Is it possible that Clinton could actually lose the Nevada caucuses tomorrow?

BRIANNA KEILAR, CNN SENIOR POLITICAL CORRESPONDENT: It certainly is, Jake. Polls are tight and the Clinton campaign is afraid that the caucus format here might favor Bernie Sanders even more than polls are indicating. This is part of the reason why she's battling so hard for South Carolina and black support there. Bernie Sanders telling BET that she's just aligning herself with President Obama to court the African-American vote.

(BEGIN VIDEOTAPE) SEN. BERNIE SANDERS (I-VT), PRESIDENTIAL CANDIDATE: Show the world that democracy is alive and well here in Nevada.

KEILAR (voice-over): Today, Bernie Sanders is making a final pitch to Nevada voters before Saturday's caucuses.

SANDERS: The issue is not just who wins the Democratic nomination, the issue is whether Nevada will play a leading role in moving this country toward a political revolution which transforms this country.

KEILAR: As Hillary Clinton tries to tighten h, grip on South Carolina eight days before the first in the South primary, scoring a big Palmetto State endorsement from Jim Clyburn, a former civil rights activist and the highest ranking African-American in Congress.

KEILAR: Clinton is also running a new biographical television ad, featuring the iconic voice of actor Morgan Freeman.

MORGAN FREEMAN, ACTOR: Her work has been about breaking barriers and so would her presidency.

KEILAR: One day before Nevada Democrats caucus, Clinton is still in search of potential supporters, courting all important union support in the Silver State.

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: I am no Johnny or Janie come lately to this. I did not just discover that unions were under pressure from the Republicans and the right.

KEILAR: Suggesting that Sanders is unrealistic in his promises.

CLINTON: I'm not just making speeches and not just promising free this and free that and free everything.

KEILAR: Clinton and Sanders both facing fresh scrutiny at a Nevada town hall last night. Clinton on whether she would release transcripts of speeches she's given to financial institutions.

CLINTON: I am happy to release anything I have when everybody else does the same, because every other candidate in this race has given speeches to private groups, including Senator Sanders.

KEILAR: Sanders was pressed to respond to comments he made in 2011, raising the possibility of a progressive primary challenge to President Obama's re-election.

SANDERS: Overall, I think the president has done an outstanding job, and the idea that there can be a primary where different ideas get floated and debated, I don't think that that is terrible.

(END VIDEOTAPE)

KEILAR: Meanwhile, Bernie Sanders' brother, Larry, had some choice words for a former president, Jake, specifically Bill Clinton. He said he was a terrible president for poor people but he actually said that Bernie Sanders' brother respects Hillary Clinton, that they're not close friends but that they worked together and he does have respect for her.

TAPPER: Rather scathing edition of "The Larry Sanders show".

[16:20:01] Brianna Keilar, thanks so much.

Joining me now is Congressman James Clyburn of South Carolina. He is the dean of the state's congressional delegation and as the House assistant Democratic leader, the highest ranking African-American in Congress. And today, he endorsed Hillary Clinton after just saying a short time ago that his heart and head were in different places.

Congressman Clyburn, hold on just a sec. We have to take a very quick break. We'll talk right after this.

(COMMERCIAL BREAK)

TAPPER: Welcome back to THE LEAD.

We're back with Congressman James Clyburn who joins me just hours after announcing his endorsement of Hillary Clinton.

Congressman, thanks so much for being here.

So, you remained neutral in 2008 when it was between Clinton and Obama. What changed this time? Why pick a side?

CLYBURN: Well, I always believed that South Carolina, our party in this state, would be in much better shape so long as we could maintain our first in the south primary.

[16:25:06] And when South Carolina was granted a position in the pre- primary window, I promised them that I would not do anything that would jeopardize the credibility of the primary.

And one of the things they asked me to do is to be very careful about getting involved in one campaign or the other. So, I swore off getting involved in anybody's campaign to keep from jeopardizing that primary. This year, I held off as long as I have held off simply because I did not want to get out too far in front of the primary day.

But I decided after talking to family and friends last week that I held off long enough and I talked to Jamie Harrison, the chair of the party, and he assured me that he did not think it would be harmful for me to do it today, and so that's why we did it today.

TAPPER: And obviously, Bernie Sanders is very popular with a lot of younger voters. How do you think Hillary Clinton is going to do in South Carolina and what do you say when and if younger people come over to you and say, why not Bernie?

CLYBURN: Well, I'll be glad to tell them exactly why I selected Secretary Hillary Clinton over Senator Bernie Sanders. I know both of them very well. I have worked with them. This is my 24th year in the Congress. I have worked with both of them throughout all of that time.

And when you add up everything, taking a look at the resumes, a look at the set of experiences, it was just clear to me that where we are in the country today, that Hillary Clinton as a former first lady of the country for eight years, secretary of state for four years, first lady of a state coming out of law school, coming to the south, working among those of us who were trying to find various -- mount challenges to the system, she has all that I think is required to make a very good president.

Now, I will tell that to young people because most of them may not be familiar with that history. They know what their parents went through, but they may not know that Hillary Clinton was standing side by side with their parents.

TAPPER: In an interview with BET, Senator Sanders said that Clinton is trying to embrace President Obama, quote, "as closely as she can so she can win support from the African-American community." What do you think of that charge?

SANDERS: Well, I don't think that I ought to get in the back and forth between them. I think that their campaigns are good campaigns. They are free to do whatever they think is necessary to win favor.

But I believe, as I said, that Hillary Clinton's resume speaks for itself, her involvement. I mean, I suspect that when she first came south to help those juveniles who were being jailed with adults, I doubt very seriously whether Barack Obama was being thought about at that time.

So, what motivated her then? What motivated her to line up with Marian Wright Edelman to run the Children's Defense Fund? What motivated her as first lady and try to get universal access to health care and settling for the state children's health insurance plan?

Those are the kind of programs and priorities that are important to the African-American community and when they know about it, it wouldn't amount to much how tightly she might hug Barack Obama.

TAPPER: Obviously, you think Hillary Clinton is more electable in November theoretically than Bernie Sanders would be. Do you have concerns, however, about how electable Bernie Sanders might be if he does get the nomination? Would that make it easier for the Republicans to take the White House?

CLYBURN: Well, you know, there's a theory that that's true. Both of them have assets. Bernie quite frankly has ignited a flame. He has the emotions with him across the board and that's a good thing.

I think that as I said Hillary has experiences and the resume. Those are good things. So, both candidates bring strengths -- would bring strengths to the ticket. I just think that our chances to be successful are greater with Hillary Clinton by far.